1. Field of the Invention
The invention relates to injection molding, and particularly to a nozzle sealing assembly for edge-gated injection molding nozzles.
2. Background of the Invention
Injection molding is a common manufacturing practice. Various articles of commercial value such as plastic bottles, toothbrushes, and children's toys, are made using well-known injection molding techniques. Injection molding generally involves melting a material, which is often plastic, then forcing the melt stream at high temperatures and pressures through one or more gates into a mold cavity. The melt cools in the shape of the mold cavity, which is opened to eject the finished part.
The melt is supplied from a machine nozzle, injected into a heated manifold and distributed to the mold cavities through heated nozzles. The heated nozzles are seated within bores in a mold plate that forms the cavities. The mold plate is cooled so that melt injected into the cavities can be adequately cooled prior to ejection. However, because the nozzle is heated and the mold plate is cooled, heat from the nozzle is drawn from the nozzle into the mold plate, which can create difficulty in maintaining the melt at an optimum temperature in the nozzle. As a result, it is often desirable to configure the injection molding system to reduce heat transfer from the nozzles to the mold plate, especially proximal to the mold gates, while still maintaining an adequate seal between each nozzle and a respective mold gate.
Front-gated nozzles often include an alignment collar and a transfer seal to maintain the position of the nozzle in the mold plate and to provide a seal between the nozzle and the mold plate. In some systems, the alignment collar and transfer seal suspend the nozzle body within a bore in the mold plate so that there is no direct contact between the nozzle body and mold plate. To further reduce heat transfer between the nozzle and the mold plate, the alignment collar and transfer seal are constructed from materials that are less thermally conductive than the nozzle body or the mold plate, and/or they are configured to reduce the contacting surface area between the components. During mold cycles the temperature of the injection molding system components fluctuate resulting in thermal expansion and contraction of those components. During the temperature cycles, sealing between the nozzle and the mold gate can be maintained by sliding contact between the transfer seal and the mold plate.
Some molding operations require edge-, or side-, gated nozzles. Edge-gated nozzles are used when a mold cavity is spaced radially from the longitudinal axis of the nozzle and melt must be distributed from the nozzle transversely with respect to the longitudinal axis of the nozzle body. Edge-gated nozzles employ one or more nozzle tips extending radially outward from the nozzle body to provide a path for melt to flow radially outward from the nozzle body.
One approach for providing a seal between a nozzle tip and a mold gate in edge-gated nozzles is to utilize individual edge gate seals or inserts that contact the mold plate adjacent to the mold gate. The gate seals are configured to slide with respect to the mold plate during thermal expansion. A disadvantage of such seals is that they form a thermal conduction path between the nozzle body and the mold plate close to the mold gate. In addition, it has been found that allowing melt to flow into a gap between the nozzle tip and mold plate may be beneficial and such thermal seals do not allow for such a gap.
Another device utilizing individual seals employs a nozzle tip that includes a sealing flange spaced from the tip outlet by an annular recess. The sealing flange has a contacting surface that is configured to contact the mold plate and seal around the mold gate. The outlet of the tip is recessed so that a gap is formed between the portion of the tip where the outlet is located and the mold gate when the sealing flange contacts the mold plate. As a result, a small cavity is formed between the tip and the mold plate that is filled with melt during operation. Although the device provides the benefit of the gap between the tip and mold plate, the proximity of the sealing flange with the mold gate provides a thermal conduction path that is close to the mold gate.
Another approach for providing a seal between a nozzle tip and a mold gate in edge-gated nozzles is to utilize a single seal between the nozzle body and the mold plate at a location spaced from the nozzle tip and mold gate. In one device, a sealing sleeve that contacts both the nozzle body and the mold plate is provided. The sealing sleeve surrounds a portion of the nozzle body spaced from the nozzle tip and mold gate. A shoulder is provided on the outer surface of the nozzle body to locate the sleeve longitudinally on the nozzle body. An upper portion of the sleeve is held in place on the nozzle body by a press fit or threaded engagement with the nozzle body. A lower portion of the outer surface of the sealing sleeve is configured such that there is sliding contact between the sealing sleeve and the mold plate. A sealing ring is also provided between the sealing sleeve and the nozzle body to improve the seal between the sleeve and the nozzle body and to prohibit melt from flowing between the sealing sleeve and the nozzle body. A gap is provided between the nozzle tips and mold gates so that melt is free to flow into a cavity created between the nozzle body, sealing sleeve and mold plate. A disadvantage of such a device is that the nozzle body must be specially configured to receive the sealing sleeve, e.g., the nozzle body must include a shoulder. Another disadvantage of the device is that mounting the sealing sleeve to the nozzle body requires either an additional press fit operation or a further complicated nozzle body design.
Another device that utilizes a single seal between the nozzle body and mold plate utilizes a sealing ring stopper sleeve and a sealing ring. The sealing ring stopper sleeve is brazed to an end portion of the nozzle body and the sealing ring is slid onto the stopper sleeve so that it abuts a shoulder provided on the stopper sleeve. Although the nozzle body does not require a special configuration in such a device, manufacture of the device requires an additional brazing operation to mount the stopper sleeve to the nozzle body.